Asphalt-based roofing materials, such as roofing shingles, roll roofing and built-up roofing, are installed on the roofs of buildings to provide protection from the elements. Typically, the roofing material is constructed of materials including an inner mat such as a glass fiber mat, an asphalt-based coating which saturates the mat and coats the top and bottom, and a layer of granules embedded in the top coating. The coating usually contains a filler such as ground limestone. Roofing shingles usually have a backdust material such as silica sand on the bottom coating to prevent them from sticking together in a bundle
The quantity and composition of the materials used to make a roofing material determine, to a great extent, the performance of the resultant roofing material (e.g., weathering, cracking, blistering, algae resistance, pliability, sticking, and impact resistance). They also determine the cost to produce the roofing material. For a roofing shingle, the cost to produce the shingle is usually about 60-80% materials cost.
Current commercial roofing materials are typically produced with the same asphalt and filler throughout (top coating, mat saturant coating, and bottom coating). Thus, each material in the coating must meet more performance criteria than if different materials could be used in the different portions of the coating. This leads to compromises, typically between cost and performance, but sometimes between one performance parameter and another.
Some patents disclose roofing materials made with varied coating compositions. For example, U.S. Pat. No. 4,405,680 to Hansen discloses a roofing shingle including a mat saturated with a mixture of unblown asphalt and polymer, and coated with a mixture of a blown asphalt and filler.
U.S. Pat. No. 4,848,057 to MacDonald et al. discloses a roofing shingle including a mat saturated with asphalt, coated with a rubber-modified asphalt on portions prone to cracking and a coating asphalt on other portions, and further coated over all portions with the coating asphalt.
U.S. Pat. No. 5,488,807 to Terrenzio et al. discloses a roofing shingle including a mat saturated with asphalt, coated with a first coating asphalt, and further coated with a second coating asphalt on portions of the shingle. The second coating asphalt has greater elongation or extensibility than the first, for example by modifying the asphalt with a polymer and a plasticizer.
U.S. Pat. No. 6,120,838 to Zickell discloses a roofing shingle including a mat saturated and coated with a mixture of flux asphalt and recycled roofing material, and further coated with a polymer-modified asphalt.
In view of the current commercial roofing materials and those disclosed in the patents, there is still a need for roofing materials having coatings that are optimized as a whole for both performance and cost. There is also a need for a process for coating such roofing materials.